1. Field of the Invention
The present invention relates to a metal pipe coated with a high thermal stability layer which is characterized by excellent adhesiveness and recoatability.
2. Description of the Prior Art
Heretofore, it has been proposed to coat a metal pipe to be laid undergound with an asphalt composition in order to make it anticorrosive. However, conventional asphalt compositions possess disadvantages in that they can easily be peeled from the surface of the metal pipe or they are subject to deterioration which decreases their anticorrosiveness. Accordingly, in order to avoid serious damage, a metal pipe possessing excellent anticorrosiveness, safety and durability is desired. This is especially true of metal pipe containing electrical cable such as telephone cable or metal pipe used for feeding gas.
It has been proposed to coat the metal pipe with a composition comprising asphalt, ethylene-vinylacetate copolymer, styrene-butadiene rubber and rosin or petroleum resin in order to improve the coating properties. However, in this case, the anticorrosiveness, stability and durability of the coated composition also deteriorate with age.
Additionally, it has been proposed to use various other coating compositions besides the asphalt composition. However, after the pipe is laid underground, cracks often form in these coated layers as a result of vibration, thereby permitting serious corrosion in the underlying pipe. Accordingly, it would be desirable to have a coated metal pipe which has excellent capability for being recoated. When a coated metal pipe is laid underground, it is exposed to changing temperatures. Accordingly, the coated layer should be effective independent of the change in temperature.
A need exists therefore for a coated metal pipe having the aforementioned desirable characteristics.